Surfactant systems which produce little or no foam and which are easy to handle and prepare are required for many different commercial and household applications. These applications include, without limitation, waste water treatment, manufacture of textiles, paper processing, machine dish washing, high pressure cleaning, carpet cleaning, laundering and hard surface cleaning. As can be appreciated, generation of unnecessary foam in such applications could interfere with any of these respective processes.
Each of these exemplary applications include conditions conducive to formation of undesirable foam. Foam generation would be expected because of the agitation and shear forces applied.
Surfactants which can be categorized as "low foaming" or "ultra-low foaming" are best suited for applications such as those described above. By low or ultra-low foaming, it is meant that very little or no foam is generated by the surfactant when agitated. Further, any foam which is generated is typically unstable and rapidly breaks down preventing accumulation of foam during the process. These types of low-foaming systems are to be contrasted with so-called "high foaming" systems in which copious amounts of foam are generated and the foam remains stable for a long period of time.
Amine oxides are known surface-active agents and would be useful in applications such as those listed above, but for the fact that they are known to be high-foaming or difficult to prepare and handle at appropriate concentrations. With respect to foaming, it is known that amine oxides are added to various compositions as foaming agents, foam enhancers or foam stabilizers. Because of these foam-generating characteristics, amine oxides are typically found in shampoos, bath preparations and hand dish detergents. Two broad classes of amine oxides typically used in these applications include dimethyl alkyl amine oxides and bis(2-hydroxyethyl) alkyl amine oxides. These amine oxides are thought of as medium to high foaming surfactants which contribute to the overall foamability and foam stability of the detergents and cleaning compositions.
Alkoxylated amine oxides are another group of amine oxides understood to be high foaming. For example, U.S. Pat. No. 3,449,431 (Swenson) repeatedly characterizes certain alkoxylated amine oxides as suds builders and not as low foaming surfactants. Such molecules would be unsatisfactory for the low-foaming applications described above.
It is known that additives, such as oil and silicone, can be added to surfactant systems or processes to reduce or eliminate foaming. However, these additives are less than satisfactory because they increase the cost of the surfactant system and can leave unwanted films or deposits on the surface to be cleaned. One object of this invention is to eliminate the need for such additives.
It should be noted that U.S. Pat. No. 5,486,315 (Tseng) claims that certain forms of dimethyl alkyl amine oxide surfactants actually produce low levels of foam. However, Tseng involves a narrow class of molecules in which the side chains (designated R.sub.1) are limited to a total of two moles of alkyl and/or hydroxyalkyl groups. These narrowly-defined structures are outside the scope of the present invention.
Another significant disadvantage with prior art amine oxides is that the compositions cannot be prepared in a highly concentrated "high actives" form which is pourable. The term "actives" refers to the amine oxide which is the active constituent of the concentrate. The prior art amine oxides exist as thick viscous gels above about 40% actives at ambient temperature, i.e., about 20.degree. C. In most industrial settings, raw materials which are liquid and pourable at room temperature are preferred over raw materials which are viscous and nonpourable at such temperatures. Obviously, pourable liquids are preferred because of the ease of handling associated with liquids. Special handling techniques are needed to handle solids and highly viscous liquids typical of prior art concentrated forms of amine oxides.
These disadvantages are apparent in commercially-available amine oxides. These products are available in a pourable form but typically include no more than 40 weight percent of amine oxide and 60 or more weight percent of water. The low level of amine oxides and high water content is required to prevent formation of gelatinous or viscous products. This is disadvantageous, however, because of the added shipping cost associated with shipping inert water with the amine oxide. Further, the opportunity to use the amine oxide in a concentrated formulation is limited.
Organic solvents, such as isopropanol or ethanol, have also been used to liquify amine oxides of the prior art. The ratio of amine oxide to solvent (as compared to the ratio of amine oxide to water noted above) is improved in that solutions of up to about 70% amine oxide and about 30% solvent can be made this way. However, use of solvents increases the cost of the product and can create safety concerns due to the flammability of the solvent. Use of such solvents may also raise environmental concerns due to the presence of volatile organic compounds (VOC). Further, a 70% actives level composition is not as desirable as a concentrate including in excess of 90% actives.
An ideal surfactant for the applications described above should have low foaming properties. The surfactant should be capable of being highly concentrated, and preferably should be a pourable liquid at room temperature. The surfactant should also have good surface-active characteristics, be compatible with other detergent ingredients and should be biodegradable. An improved surfactant with all of these characteristics would represent an important advance in the art.